Book/Report

FZJ-2018-00697

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Dämpfung und Dispersion von Erstem Schall in $^{3}He-^{4}He$ Mischungen nahe T $\lambda$

Buchal, C. (Corresponding author)FZJ*

1976
Kernforschungsanlage Jülich, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/16660

Report No.: Juel-1302

Abstract: The attenuation $\alpha$, the velocity u, and the dispersion D = u($\omega$)-u(O) of first sound have been determined in $^{3}He-^{4}He$ mixtures (molar $^{3}$He concentrations X$_{3}$ = 0, 0.070, 0.194, 0.377, and 0.517) at frequencies 2.3 kHz $\le$ $\omega/2\pi$ $\le$ 627 kHz, and in the temperature range 1 $\mu$K $\le$ $\vert$T-T$_{\lambda}\vert$ $\le$ 20 mK. From rneasured velocities we evaluate the thermodynamic velocity u(O), as well as ($^{\partial}S/^{\partial}P)_{\lambda}$, and ($^{\partial}V/^{\partial}P)_{\lambda}$. The attenuation and the dispersion are considerably reduced when the $^{3}$He concentration is increased. They are interpreteä as arising from a relaxation process occurring only below $T_{\lambda}$, and a fluctuation process occurring on both sides of the $\lambda$-transition. Both contributions have about equal strength anti have to be added for T < T$_{\lambda}$. Using the obtained relaxation time $\tau'$ = $\tau'_{o}$t$^{-x'}$, (with t = $\vert$T-T$_{\lambda}\vert$ / T$_{\lambda}$), and published data for the correlation length $\epsilon$', and for the second sound velocity $\mu_{2}$, we find $\tau$' = $\epsilon$'/u$_{2}$ for T < T$_{\lambda}$. The amplitude $\tau'_{o}$ increases more than one order of magnitude with increasing X$_{3}$ in the investigated concentration range. For T > T$_{\lambda}$ our absorption and dispersion data for all $\omega$ and X$_{3}$ can be scaled with functions of $\omega\tau$ over four decades of $\omega\tau$. This scaling analysis shows that the time $\tau$ characterizing the criticalattenuation and dispersion at T > T$\lambda$ has the same temperature and concentration dependence as the relaxation time $\tau$' at T < T$_{\lambda}$; these two times differ at most by a constant multiplicative factor. The frequency dependences in the critical region ($\omega\tau$ > 1) scale as $\alpha$ « $\omega^{1+y}$ and D « $\omega^{y}$ with y = 0.10 for X$_{3}$ $\le$ 0.2; the exponent y increases at higher X$_{3}$.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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